I don't know if this will solve your problem, but you could try this: https://www.amazon.com/BEHRINGER-Audio-Interface-1-Channel-UM2/dp/B00EK1OTZC It has a couple instrument inputs and a line output, it would just need USB power. You wouldn't even need to plug it into your computer if you turn on the "Direct Monitor" button. I have one and it's a decent interface, but it won't give you distortion.
If you add this: https://www.amazon.com/Behringer-Ultragain-MIC100-Audiophile-Preamplifier/dp/B000CZ0RME with the above you could have tube distortion that gets converted to a line output.
or...
I have one of these: https://www.amazon.com/Laney-IRTPULSE-Irt-Pulse-Preamp-USB/dp/B00U6BXCX0 it is more expensive, but is all tube and has a headphone and line output (https://www.amazon.com/CableWholesale-4-Inch-Phono-Adapter-30S1-16260/dp/B000I98Z50), that you could connect to the input on the crack. It can also work without a USB connection.
Anyway, just a couple options.
This is a good idea that I hadn't though of though, I might have to try it!